1. Field of the Invention
The invention pertains to a device wherein in the area of lock cylinders, both mechanical and electrical components are used, which, when a key is used to operate the lock, activate or deactivate electrical functions by way of the electrical switching device. The lock cylinder consists of a stationary cylinder housing with a rotatable cylinder core inside, which can be rotated by a properly fitting key. The mechanical components comprise a key channel which accepts the key, tumblers in the cylinder core, and a locking channel for the tumblers in the cylinder housing. The electrical components include at least one permanent magnet on the circumference of the cylinder core and a sensor in the cylinder housing, which, when the key is used to operate the cylinder core, responds to the permanent magnet. The sensor is connected to an evaluator, which activates the electrical switching device when the key operates the lock. The lock cylinder of a device such as this is preferably installed as a steering lock in the area of the steering column of a motor vehicle, and the electrical switching device contains the electronics of the engine. Devices of this type are used to protect the motor vehicle against theft. The device is then referred to as an "electronic device for preventing a vehicle from being driven away".
2. Description of the Related Art
A device such as this is known from U.S. Pat. No. 5,186,031. In this device, the vehicle is protected from theft even after the thief has pulled the cylinder core of the lock cylinder axially out of the cylinder housing in order to manipulate the interior of the cylinder housing. In this known device, the cylinder core has a radially spring-loaded retaining element, which, when the cylinder core is installed, snaps behind a shoulder on the housing. It is thus easy to install the cylinder core axially in the cylinder housing. When the cylinder core is torn out axially by the thief, the retaining element destroys the electrical connections of the sensor in the cylinder housing and thus makes the device inoperable. This anti-theft protection fails, however, when it is possible to use a break-in tool to move the spring-loaded retaining element into its release position with respect to the cylinder housing. In the case of devices in which the cylinder core is not connected to the cylinder housing by means of a snap-in attachment such as this, however, no anti-theft protection is present at all. The reason for this is as follows.
The anti-theft protection of vehicles equipped with these types of lock cylinders consists in that there are a large number of different lock cylinders, each of which has a different set of tumblers in the cylinder core. The cylinder core can thus be rotated only by a certain key which fits this cylinder core. Whereas the cylinder housing has a uniform design, there are many different keys, and each key fits only the corresponding, individual arrangement of tumblers in the cylinder core. To break open a lock equipped with a lock cylinder for which the proper key is not available, it is sufficient for the thief to tear out the cylinder core and replace it with a new cylinder core, for which he has the proper key. It makes no difference to the cylinder housing that the original cylinder core has been replaced by a new one for which the thief has the proper key. This theft strategy also functions in the case of the known device in which the cylinder core has a permanent magnet and the cylinder housing has a sensor, because the new cylinder core bought with the key also has a permanent magnet, which is then able to perform the same functions in the interior of the cylinder housing as the permanent magnet of the torn-out cylinder core. The known device thus does not offer adequate protection.